Casehardening



W. J. MERTEN CASE hARDENING Filed Dec. 2, 1920 Feb. 2 1926.

, un HHHHU II. lllllc INVENTOR zw'rzzfwrfm. BY

A'i'TORNEl WITNESSES: g QW l1 EEEREZEN, 0h PITTSBURGH, PENNSYLVANIA.

GASEEDEITING.

application filed December 2, 1920. Serial No. 42?,753,

51% all whom it may concern:

it known that l, W'rraaasr al Mnn'rnn, citizen of the llnited States, and a resident of Pittsburgh, in the county of Allegheny and State of Pennsylvania, have in" vented a new and useful improvement in Qasshardening, oi which the following is a specification,

invention relates to case hardening, more particularly to a method of case liar suing which is adapted to rapidly and uniy case harden metal articles, even of en form, and an apparatus for pracmy new method: iilbllaifllfi', several methods have been proposed for casehardening or steel parts among which the one in general use was a method in which the articles to be hardened were packed with vea rburiaing materials in a metal box, after which the hon was tightly sealed to prevent access of air. The material was then heated to a relatively high temperatiu'e for a considerable length of time,

The results obtained in this operation were nnccitainv and it was difiocult to dupli cats predetermined result because of the non uni'iormity oi the carburizer and the last that the heat to which the steel was exosed could not be readily controlled, owmg to the parts bein treatedbeing but indirectly exposed to t a heat. The. cost of heating was high and the metal boxes in which the articles were sealed rapidly deteriorated due to oxidation or scaling.

Another method consisted in immersing an article to be hardened in a cyanide bath heated to a rather high temperature. This method was fairly efiective with small articles where only surface hardening was desired but was ob'ectionable in that a uni form case hardening could not be produced and the articles immersed in various parts of the bath were unequally penetrated. @lten the article was heated to ahigh temperature and then plunged into a container filled with powdered cyanide, or such powdered salt was sprinkled on the hot metal article. This method produced a case which was very superficial and bad but little resistance to wear,

My invention obviates the disadvantages oi the prior processes, it being among the objects thereof to devise a method wherein the article to be treated is uniformly case hardened in a very simple and eficicnt manner.

lln practicing my invention, ll provide a source of a suitable gaseous material, such as cyanogen gases, which are allowed to W come in contact with the article to be treated at an elevated temperature, whereby the article absorbs the gases uniformly, terming a uniform case thereon. in order to conserve the cyanogen gases which are relatively expensive, I have devised an appa-= ratus in which such gases are returned to the system, after coming in contact with the article.

In this manner, I am enabled. to utilize, W

or penetration than with the use of other W methods and l also avoid the disadvantages inherent 1n the use of a poisonous substance, such as cyanogen.

In the accompanying drawings forming a part hereof, the single figure is a view in m vertical section of an apparatus constructed in accordance with my invention and adapted to the practice of my new method."

The receptacle 1, here shown as apot, is

mounted in the furnace 2, fixed to any suit- 35 able support, such as legs 3., A carburizing medium 4, which may be a cyanide or a forrocyanide or similar substance, is laced in the receptacle 1, which is hea by any suitable means, such as a gas burner 5. 90

Vertically above receptaclel and in communication therewith, is a furnace chamber 6 having walls 7 and a heating element 8, preferably an electrical resistance element,

is imbedded. in walls 7. The furnace thus W formed is adapted to heat the article to be treated to the proper hardening temperature.

An extension 9 is formed above wall 7 and has embedded therein a bracket 10 1 which holds a hook or similar member ll adapted to carry an article 12 to be treated, here show-n as a shaft. A door 13, hin ed at 14, and having a handle 15, is provi ed to allow access to the furnace for the removal or insertion of various articles. A cover 16, which is generally of the bell type, has a cable 17 secured thereto and runnin over pulleys 18, the other end of said ca le being attached to the door 13 at i through t e point 19. A stack 20 is provided for withdrawing waste gases.

The upper portion 21 of the vertical fur.-

nace is provided with a tube or conduit'22 having a water jacket 23 surrounding it'and.

being connected to a fan or blower 24,

An example of the operation of my de vice for case hardening. is as follows.: Sodium cyanide is placed in receptacle 1 and heated by means of gas burner 5 to a temperature above its boiling point, about 800 C., the door of the furnace and the bell 16 both being closed and the fan 2& being in operation. An article to be. treated is placed in furnace 6 and heated electrically by means of resistance element 8 to a temperature abpve the upper critical point, about 900 C. Cyanogen gases are produced by the volatilization and decomposition'of the sodium cyanide and pass up into chamber 6, surrounding article 12, which. is

at such a high temperature that it rapidly absorbs the gases, case hardening the surface thereof. Unabsorbed gases pass upwardly, are drawn into conduit 22, and are cooled by water jacket 23 in order to prevent corrosion'of the fan 'or blower member. The gases are then returned to receptacle 1 blower 24 where they bubble liquid sodium cyanide, agitating the same, thus rendering the evolution of cyanogen gases more cfficient and avoiding wasting any of the unabsorbed gases.

When it is desired to remove an article that has already been treated, it is not necessary to completely suspend the operation of Y the apparatus, but door 13 is opened, thereby removing cover16 from the top of the furnace, inducing a draft through the furnace door opening and stack 20, removing the poisonous gases through the stack, thus obviating any danger to the operator. If desired, cover 16 may first be opcned, blower 24 stopped, and then door 13 opened to charge or discharge the furnace.

My apparatus is very simple, the operation thereof does not require skilledworkmorn-and the coating producedron an article is uniform, the thickness'thereof being a function solely of the time of exposure to the gases at any given temperature. The ga under pressure, coming in contactwith the article to be case hardened, attacks the surface very vigorously, causing more rapid and deeper penetration. There is practical-- )ly no danger of the poisonous gas escaping 'into the space around the apparatus since,

if the pressure in the furnace becomes excessive, cover 16 Wlll be'unseated allowing the gases to enter the stack 20.

means for allowing said. gases to Although I have described my invention as embodied in a specific apparatus, it is to be understood that such description is intended to be illustrative only and does not limit my invention since it is obvious that various-changes may be made Within the scope thereof. For instance, instead of using a bracket-to suspendart-icles to be treated, I may form a id or series of grids in chamber 6 upon WllCh various articles are placed, and I may use a different arrangement for allowing the escape of the oisonous gases when the operator opens t e furnace door. Various other materials for carburizing may be used and I consider my invention as not limited to the use of sodium cyanide but various other materials, such as ferroand ferri-cyanides and other gas producing carburizers, are also adapted for my purpose.

I claim as my invention:

1. A method of case hardening which comprises heating a cyanide to produce cyanogen gases, conducting said gases to an article or articles to be treated and returning th unabsorbed gases to their source.

2. A method of case hardening which comprises producing carburizing gases, conducting said gases to an article or articles to be treated and returning the unabsorbed gases to their source.

3. A method of case hardening which comprises heatin a cyanide to produce cyanogen gases, allowing said gases to come in contact with an article to be-treated, and agitating said cyanide.

4. A method of case hardening which I comprises heating a cyanide to produce cyanogen gases, ailowing said gases to come in contact with an article to be treated, and agitating said cyanide by bubbling unabsorbed gases therethrougl p 5-. An apparatus for case hardening comrising a furnace for heating an article to he (treated, means for generating gases, me in contact with said article, and a con uit for returning unabsorbed gases to the source of supply.

6. An apparatus prising a furnace for heating an article to be treated, means for generating gases, means for allowing said gases to come in contact with said article, and means for pre-' venting escape of said gase into the space surrounding said apparatus.

7. An apparatus for case hardening comprising a furnace for heating an article to be treated, a receptacle adapted to hold gasproducing material, means for heating the same to generate gases, means for allowing said gases to come in contact with said article, and a conduit for returning unabsorbed gases to said-receptacle.

8. An apparatus for case harden ng comfor case hardening comprising a vertical furnace, a receptacle adapted to hold gas-producing material at the lower end thereof, means for heating said receptacle to generate gases, means.

furnace, a conduit in said top for leading off said gases, and means for returning the same to said receptacle.

In testimony whereof, I have hereunto subscribed my name this 30th day of November 1920.

WILLIAM J. MERTEN. 

